Mobile wireless local area network and related methods

ABSTRACT

A wireless local area network adapted for use by users traveling on a mobile platform such as an aircraft. The network includes a network server located on the mobile platform, and at least one network access point connected to the server and accessible wirelessly by at least one user portable electronic device over one of a plurality of non-overlapping network frequency channels. The RF characteristics of this wireless network are specifically tailored to meet applicable standards for electromagnetic compatibility with aircraft systems and RF exposure levels for passengers and flight crews.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/878,674 filed on Jun. 11, 2002 now U.S. Pat. No. 6,990,338. Thedisclosure of the above application is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to communication systems onboard mobile platforms such as aircraft and, more particularly, to anon-board wireless local area network (WLAN) accessible by passengers'portable electronic devices such as laptop computers.

BACKGROUND OF THE INVENTION

Mobile network systems have traditionally been limited in bandwidth andlink capacity, making it prohibitively expensive and/or unacceptablyslow to distribute broadband data and video services to all passengerson a mobile platform such as an aircraft, boat or train. There is greatinterest in making such services available to users on mobile platforms.A system for supplying television and data services to mobile platformsis described in co-pending U.S. patent application Ser. No. 09/639,912,the entire disclosure of which is incorporated herein.

The system described in application Ser. No. 09/639,912 providesbi-directional data transfer via satellite communications link between aground-based control segment and a mobile RF transceiver system carriedon each mobile platform. Each user on each mobile platform is able tointerface with an on-board server by using a laptop, personal digitalassistant (PDA) seat-back-mounted computer/display or other computingdevice. Each user can independently request and obtain Internet access,company intranet access, stored video and audio programming and livetelevision programming.

It would be desirable to provide passengers with wireless connections tonetwork services available on mobile platforms such as aircraft. Thereare concerns, however, about the possibility of interference to aircraftsystems from portable electronic devices (PEDs) that might be used bypassengers to make wireless connections to an on-board network. Ofparticular concern is the possibility of PED interference duringcritical phases of flight, for example, during takeoff and landing.There also are concerns that such networks might expose passengers andflight crews to radiated RF fields exceeding recommended health andsafety limits for RF exposure.

Generally there are two types of PEDs: (1) intentional transmitters,which must transmit a signal in order to accomplish their function (e.g.cell phones, two-way radios, pagers and remote-control devices), and (2)non-intentional transmitters, which do not need to transmit a signal toaccomplish their function, but nevertheless emit some level of radiation(e.g. laptop computers, compact disk players, tape recorders andelectronic hand-held games). The Federal Aviation Administration (FAA)has not issued certification regulations for PEDs. The FAA does,however, restrict the use of PEDs on commercial airlines. FAA advisorycircular AC91.21-1 paragraph 6.a (7) states that, unless otherwiseauthorized, use of PEDs classified as intentional transmitters should beprohibited during aircraft operation. General Operating and FlightRules, 14 CFR 91.21(b)(5) (“Portable Electronic Devices”) prohibits theoperation of a PED on an aircraft, unless the aircraft operator hasdetermined that the device will not cause interference with thenavigation or communication systems on board the aircraft. Thus it isdesirable to provide a wireless network that can be determined to beaccessible by passenger-operated PEDs without causing such interferenceand thus could be authorized for on-board use. It also is desirable toprovide an on-board wireless network that produces RF emission levelswithin recommended health and safety limits.

SUMMARY OF THE INVENTION

In one preferred form, the present invention provides a wireless localarea network adapted for use by users traveling on a mobile platformsuch as an aircraft. The network includes a network server located onthe mobile platform, and at least one network access point connected tothe server and accessible wirelessly by at least one user portableelectronic device over one of a plurality of non-overlapping networkfrequency channels. This wireless local area network can provide two-waycommunication, data and entertainment for aircraft passengers, cabincrews and flight crews. Such information may be obtained via e-mail,internet, company intranet access, and/or from data stored on board oroff board the aircraft. The RF characteristics of this wireless networkare specifically tailored to meet applicable standards forelectromagnetic compatibility with aircraft systems and RF exposurelevels for passengers and flight crews.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a view of a wireless LAN (“WLAN”) adapted for use in a mobileplatform such as an aircraft;

FIG. 2 is a plan view of WLAN cells in an aircraft passenger cabin,shown from above the overhead area;

FIG. 3 is a graph of E-field strength of emissions versustransmitter-to-victim distance for a WLAN;

FIG. 4 is a view of a portion of a passenger cabin, shown from above theoverhead area, in which more than one user PED is in use; and

FIG. 5 is a graph of margins of compliance with FCC OET Bulletin 65 forthe effect of adjacent laptops on RF exposure versus distance fromtransmitter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. As described below, the present invention inone embodiment is directed to a wireless LAN (“WLAN”) for use in amobile platform. The mobile platform could include an aircraft, cruiseship or any other mobile vehicle. Thus the reference to the mobileplatform as an aircraft throughout the following description should notbe construed as limiting the applicability of the WLAN 10 and/or thepresent invention to only aircraft.

A preferred embodiment of a wireless LAN for use in a mobile platformsuch as an aircraft is indicated generally by the reference numeral 10in FIG. 1. The WLAN 10 includes an Ethernet router/server 14(hereinafter “server”) wired to a plurality of access points 18 via atleast one switching device such as an Ethernet switch 22. In theembodiment shown in FIG. 1, the server 14 is connected to a transmitantenna, in this example, a transmit phased array antenna system 26, andto a receive antenna, which in this example comprises a receive phasedarray antenna system 30. The antenna systems 26 and 30 provide fortwo-way communication via satellite link between the WLAN 10 and aground based network segment, as described in co-pending U.S. patentapplication Ser. No. 09/639,912. The server 14 can interface with othersystems, for example, with in-flight entertainment and/or telephoneservice systems. In another embodiment the WLAN 10 operates standalonein the mobile platform.

Each access point 18 has an antenna 34 located, for example, in thepassenger cabin overhead. Each access point 18 is configured to transmitRF signals to, and receive RF signals from, one or more PEDs 38 carriedon board by passengers. Such PEDs are fabricated for wireless use orhave a wireless adapter antenna (not shown) and can include laptops,PDAs or the like. The access point antenna 34 may be, for example, anomni-directional or patch antenna. The number and location of accesspoints 18, and the number of PEDs 38 associated with an access point 18,can vary as further described below.

An exemplary arrangement of access point antennas 34 relative to PEDs 38is shown in FIG. 2, which is a plan view of a portion 76 of an aircraftpassenger cabin. Two access points 18 (not shown in FIG. 2) andassociated antennas 34 are located in the overhead. Although an accesspoint 18 could be located outside the cabin overhead, locating it closeto its antenna 34 in the overhead reduces the length of a cableconnection between them. Each access point 18 broadcasts over a cell 80that includes eighteen seats 84. Other cell sizes and numbers ofassociated seats can be used, as further described below. Factorsinfluencing the sizes and numbers of cells 80 include seat width 92,seat pitch 96, distance 100 between antennas 34, interior width 104 ofthe cabin, and the width 108 of each of the rows of seats 84.

The WLAN 10 operates in the 2.40 to 2.483 GHz ISM band, which isdesignated for unlicensed commercial or public use. Other licensed orunlicensed bands above 2.4 GHz, for example, the ISM 5.725 to 5.875 GHzband, could also be used. The WLAN 10 is configured in conformance withthe IEEE 802.11b (High Rate) standard. The invention is not so limited,and other bands, standards, and protocols can be used. Each access point18 communicates with the server 14 through the Ethernet switch 22 atfull available bandwidth. The WLAN 10 utilizes Direct Sequence SpreadSpectrum (DSSS) transmission between each access point 18 and itsassociated user PEDs 38. That is, the spectrum is divided into threenon-overlapping frequency channels of approximately 22 MHz each. It iscontemplated that other spread-spectrum modulation methods also could beused.

Each access point 18 is configured to communicate with PEDs 38 over oneof the three channels. For example, as shown in FIG. 1, three accesspoints 18 communicate using channels 1, 6 and 11 respectively. Adjacentaccess points 18 broadcast over different channels. For example,referring to FIG. 2, a user sitting in a cell 80 in which the associatedaccess point 18 broadcasts over channel 1 could communicate with theWLAN 10 via channel 1. Another passenger sitting in an adjacent cell 80would communicate with the WLAN 10 over channel 6 or channel 11.

Where the number of access points 18 exceeds three, each channel can bere-assigned to another access point 18 that is not adjacent to an accesspoint to which the channel is already assigned. For example, sevenaccess points 18 located sequentially along the aircraft aisle overheadcould use channels 1, 6, 11, 1, 6, 11 and 1 respectively. Thus use ofeach of the three channels can be distributed spatially over theaggregate of cells 80, for example, to users distributed over the entirepassenger cabin. Of course, the channels can be distributed over aplurality of cells in many different ways. Additionally, a connecteduser PED 38 can roam, e.g. as supported by the IEEE 802.11b protocol.That is, a WLAN 10 connection established with a user PED 38 in one cell80 over one channel can be maintained over another channel if the userPED 38 roams to other cells. For example, a user carrying a PED 38 canwalk, from one cell 80 in which the PED is connected to the WLAN 10 viachannel 1, into an adjacent cell 80 in which, for example, channel 6 isbeing used, and maintain the connection to the WLAN 10.

Communication between the PEDs 38 and the access points 18 ishalf-duplex. That is, in each frequency channel, at any one time eitherthe access point 18 or one user PED 38 can transmit. PEDs communicatevia CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance). Thatis, a PED 38 checks for a quiet channel before transmitting to itsassociated access point 18. If the channel is busy, the PED waits arandom amount of time and then retransmits. Several PEDs 38 couldtransmit simultaneously when contending for channel use. If a collisionof their signals is detected, each of the transmitting PEDs “backs of”and waits a random time period before retransmitting. Eventually one PEDgains control of the channel and transmits.

The WLAN 10 is configured such that only access points 18 and PEDs 38that meet applicable interference, health and safety requirements areallowed to operate within the network. PEDs that do not comply with suchstandards are excluded from connecting to the WLAN 10. Morespecifically, and for example, according to IEEE 802.11b protocol, eachtype of PED 38 that has passed testing for compliance with applicableinterference, health and safety standards is identified in the MAC(Media Access Control) layer of the WLAN 10. Thus it can be determinedat each access point 18 whether a remote PED 38 has been predeterminedto be suitable for connection to the WLAN 10. If the PED is one that hasbeen approved for connection, it is allowed to connect to the network;if not, the PED request for network access is ignored.

Configuring a WLAN for use in aircraft entails consideration of avariety of factors, including those related, for example, to aircraftand passenger safety. Not all of such factors, however, are unique toaircraft. Thus many of the considerations for configuring an aircraftWLAN also pertain to configuring a WLAN for use in other types of mobileplatforms. Embodiments of a mobile WLAN as described above can beconfigured in accordance with the following assumptions, determinationsand considerations.

Distance Assumptions and Far Field Calculations

Emissions by 802.11b wireless LANs can be treated as a far fieldproblem. The wavelength, λ, at 2.4 GHz is 0.125 meters. The far fieldlimit is approximated by 2*d²/λ where “d” is the largest dimension ofthe transmitting antenna. For a typical omni-directional or patchantenna utilized at a wireless access point mounted, for example, in theoverhead in an aircraft passenger cabin, the largest dimension isassumed to be approximately 9 inches or 0.23 meters. The far field limitfor such an antenna 34, then, is approximately 0.85 meters.

A typical user PED 38 PCMCIA adapter antenna is assumed to have alargest dimension of 2 inches or 0.05 meters. The far field limit forsuch an antenna, then, is approximately 0.04 meters. Based on theforegoing assumptions and determinations, all WLAN 10 emissions morethan one meter from an access point antenna 34 or more than fourcentimeters from a user PED 38 antenna can be treated as being in thefar field.

Non-coaxial aircraft system cables can be lossy at the frequenciescontemplated for use in the airborne WLAN 10. Therefore, possibleeffects of WLAN-radiated field levels at line replaceable units (LRUs)of an aircraft system are considered. An access point antenna 34transmitting to users in an aircraft passenger compartment would beprevented by its ground plane (not shown) from radiating at significantlevels into the overhead compartment. Access point antenna 34 emissions,then, are investigated primarily for their effect on equipment inavionics bays under the floor or in the sidewalls of the aircraft. Theuser PED 38 antennas could radiate into both the overhead and underfloorareas of the aircraft. System LRUs can be installed in equipment baysand/or in the overhead throughout the aircraft. Therefore the minimumdistance from an operating access point antenna 34 or a user PED 38adapter to an airborne system LRU is assumed to be one meter.

Field Strength Levels

The following methodology is used to evaluate field strength levels forboth aircraft system RF susceptibility and for RF exposure compliance.For the following analysis of field strength levels, it is assumed thata transmit antenna on either an access point or user adapter has amaximum gain value of 2.2 dBi (numerical value 1.66), and that transmitcable losses are zero dB. The far field radiated power density is givenby:P _(d)=(P _(t) *G)/(4*π*D ²)   (1)where “P_(t)” is transmitter power at antenna input in watts, “G” isnumerical gain of the transmit antenna relative to an isotropic source,and “D” is distance from center of transmit antenna to measuring pointin meters.

The E-field in free space is given by:E(v/m)=SQRT (P_(d)*377), or   (2)E(dBuv/m)=20 LOG₁₀(E*10⁶)   (3)where “E”

Where “E” is the E-field strength in volts per meter and “dBuv/m” isfield strength in dB above 1 microvolt per meter. Referring to FIG. 3,test data indicate that, for a single transmitter, transmitted powerlevels of both 1 and 3 milliwatts with a nominal unity gain (0 dBi)transmit antenna, the field strength is at or below 110 dBuv/m (0.3volts per meter) for all distances greater than one meter. For multipletransmitters operating simultaneously using 802.11b protocol, fieldstrength levels are analyzed as further described below.

Maximum Permissible Exposure (MPE) Levels

A 802.11b network operates in the 2.4 to 2.483 GHz ISM band. The IEEEC.95.1-1999 standard for human exposure to RF electromagnetic fieldsspecifies a maximum permissible whole body exposure (MPE) level for thisfrequency region in an uncontrolled environment of f/1500 mw/cm2averaged over 30 minutes, where f is frequency expressed in MHz. Theworst case or minimum value is at the lower end of the frequency bandwhere MPE=2400/1500=1.6 mw/cm2 or 16 w/m2. The FCC requirement asspecified in OET Bulletin 65 for this frequency range is 1.0 mw/cm2 or10 w/m2 averaged over 30 minutes. Although the European CENELEC ES59005maximum allowable RF exposure levels are less stringent than the FCClimits, the more conservative FCC requirements for compliance are usedherein.

Maximum 802.11b Radiated Field Strengths

It is assumed that over any 30-minute interval the separation distancefrom an individual to an access point antenna 34 in the overhead is 1.0meters. Table 1 below describes 2.4 GHz WLAN radiated emissions attransmit powers from 1 to 100 milliwatts and at a transmitter-to-victimdistance of 1 meter.

TABLE 1 2.4 GHz WLAN Radiated Emissions Victim to Transmitter Distance =1 m lambda = 0.125 m Assume Tx antenna gain (dBi) = 2.2 = numeric EffArea = 0.001875 m{circumflex over ( )}2 1.659587 short dipole TransmitTx Power Tx Field Tx Field Received Power Density Strength StrengthReceived Power (mw) w/m{circumflex over ( )}2 v/m dBuv/m Power w dBm  10.000132066 0.223134 106.9713 2.48E−07 −36.06209  3 0.000396197 0.386479111.7425 7.43E−07 −31.29087  5 0.000660329 0.498943 113.961  1.24E−06−29.07239 10 0.001320657 0.705612 116.9713 2.48E−06 −26.06209 200.002641315 0.997886 119.9816 4.95E−06 −23.05179 30 0.003961972 1.222155121.7425 7.43E−06 −21.29087 50 0.006603286 1.577796 123.961  1.24E−05−19.07239 100  0.013206573 2.23134  126.9713 2.48E−05 −16.06209

Referring to Table 1, test data indicate that an 802.11b systemradiating at 3 mw maximum output power will generate a radiated powerdensity of 4×10−4 w/m2 at the distance of 1 meter from the access pointantenna 34. This power density is 4.0×10−5 times the maximum allowed FCClevel, which is equal to a margin of 44 dB.

It is possible for tall individuals to be within 0.25 meters of anoverhead access point antenna 34 in a single-aisle aircraft or for auser to be within 0.05 meters of his/her PED 38 antenna. Table 2 belowdescribes 2.4 GHz WLAN radiated emissions at transmit powers from 1 to100 milliwatts and at a transmitter-to-victim distance of 0.05 meter.

TABLE 2 2.4 GHz WLAN Radiated Emissions Victim to Transmitter Distance =0.05 m lambda = 0.125 m Assume Tx antenna gain (dBi) = 2.2 = numeric EffArea = 0.001875 m{circumflex over ( )}2 1.659587 short dipole Trans- mitTx Power Tx Field Tx Field Received Power Density Strength StrengthReceived Power (mw) w/m{circumflex over ( )}2 v/m dBuv/m Power w dBm  10.052826292 4.46268 132.9919 9.9E−05 −10.0415  3 0.158478876 7.729588137.7631 0.000297 −5.27027  5 0.26413146  9.978856 139.9816 0.000495−3.05179 10 0.52826292  14.11223 142.9919 0.00099  −0.04149 201.056525839 19.95771 146.0022 0.001981 2.968814 30 1.584788759 24.4431147.7631 0.002971 4.729727 50 2.641314598 31.55591 149.9816 0.0049526.948214 100  5.282629196 44.6268 152.9919 0.009905 9.958514

Table 3 below describes margins of compliance with FCC OET Bulletin 65for worst-case exposure with access points separated by 3 meters andwith multiple transmitters.

TABLE 3 Worst Case Exposure with Multiple Transmitters ComplianceMargins for FCC OET Bulletin 65 Reqmt Seat spacing (row) = 0.8 m in =31.496 Self Dist = 0.05 m Seat spacing (side) = 0.5 m in = 19.685 FCCRqmt 10 w/m² Access Pt Spacing = 3 m Assume Tx antenna gain (dBi) = 2.2= numeric 1.659587 Single Emitter Tx Pwr = 3 Pwr Dens Distance m w/m² 0.75 0.000704 0.7 0.000809 0.6 0.001101 0.5 0.001585 0.4 0.002476 0.30.004402  0.25 0.006339 0.2 0.009905 0.1 0.03962   0.05 0.158479 Two &Four Adjacent Emitters + Own @ 0.05 meter Tx Pwr = 3 mw Four + own Two +own Single Dist-TX#1 Two + own Margin Margin Four + own Margin mDist-TX#2 m w/m² dB dB w/m² dB  0.25 0.75 0.165522 17.81143 41.522110.166931 17.77463 0.3 0.7 0.16369 17.85979 40.92285 0.165098 17.822570.4 0.6 0.162056 17.90336 39.58391 0.163464 17.86577 0.5 0.5 0.16164817.91428 38.00029 0.163057 17.8766 0.6 0.4 0.162056 17.90336 36.062090.163464 17.86577 0.7 0.3 0.16369 17.85979 33.56331 0.165098 17.82257 0.75 0.25 0.165522 17.81143 31.97969 0.166931 17.77463 0.8 0.2 30.041490.9 0.1 24.02089  0.95 0.05 18.00029 Exposure from Two Adjacent AccessPts Tx Pwr = 3 mw PwrDens Margin Dist-TX#1 m Dist-TX#2 m w/m² dB  0.252.75 0.006392 31.94394 0.3 2.7 0.004457 33.51002 0.4 2.6 0.00253535.96049 0.5 2.5 0.001648 37.82995 0.6 2.4 0.001169 39.32062 0.7 2.30.000883 40.53813 0.8 2.2 0.000701 41.54333 0.9 2.1 0.000579 42.373421   2 0.000495 43.05179 1.1 1.9 0.000437 43.59334 1.2 1.8 0.00039744.0075 1.3 1.7 0.000372 44.30008 1.4 1.6 0.000357 44.47446 1.5 1.50.000352 44.53241

Referring to Tables 2 and 3, test data indicate that an 802.11b systemradiating at 3 mw maximum output power will generate a radiated powerdensity of 6.3×10−3 w/m2 at the worst-case minimum distance of 0.25meters from the access point antenna 34 and 1.6×10−1 w/m2 at theworst-case minimum distance of 0.05 meters from the user PED 38 antenna.For the access point antenna 34, this power density is 6.3×10−4 of themaximum allowed FCC level, which is equal to a margin of 32 dB. For theuser PED 38 antenna, this is 1.6×10—2 of the maximum allowed FCC level,which is equal to a margin of 18 dB.

Contribution from Multiple WLAN Sources

The contribution of multiple WLAN RF emission sources simultaneouslytransmitting is addressed next. Referring to FIG. 2, the width 92 ofeach seat 84 is assumed to be 0.5 meters. The seat pitch 96 is assumedto be 0.8 meters (32 inches) and the distance 100 between access pointantennas 34 is assumed to be a minimum of 2.5 to 3 meters. Thus it isassumed that the worst-case RF levels are generated by multiple userstransmitting via PEDs 38 while sitting in the seats 84 or otherwiseclosely spaced in the cell areas 80. It is assumed that the user PEDs 38transmit simultaneously when they contend for the RF medium aspreviously described. Such simultaneous transmissions occur only forshort periods of time (before one PED is granted access to transmit),compared to the 30-minute exposure time described above in connectionwith the FCC maximum allowed level of power density. The possibilitynevertheless is considered, however, that such transmissions mightgenerate RF signal levels that might interfere with airframe systems. Italso is assumed that these asynchronous sources are in phase and thattheir transmitted signals will add constructively, even though this isunlikely.

A layout of a plurality of PEDs 38 in adjacent seats 84 is shown in FIG.4. The predominant source of EMI is likely to be a user's own laptop 38antenna, which was assumed above to be at the worst-case distance of0.05 meters from the user. FIG. 5 shows margins of compliance to FCCemission requirements for a single laptop and for a laptop adjacent toother laptops. At the assumed seat width of 0.5 meters, the effect ofone adjacent emissions source diminishes as the user approaches (e.g.leans toward) the other source. The seat pitch is assumed to be 0.8meters (32 inches). Therefore the contributions from sources in seatrows in front of or behind the subject will not significantly affect themargin of compliance. As shown in Table 3, including two more sources at0.75 meters (directly in front and in back of the subject laptop andtransmitting at 3 mw) to the two sources in the same seat group plus thesubject's laptop will only change the margin for RF exposure compliancefrom 17.81 to 17.77 dB.

Radiated Cell Dimensions

Cell size is determined based on the contemplated power level for theWLAN, the aggregate bandwidth contemplated to be available, and thenumber of users contemplated to share the bandwidth. For example, in theembodiment shown in FIG. 2, a cell population of 3 rows includes 18seats per access point. Such could be the case for a narrow bodyaircraft, e.g. a Boeing 737 or 757. A cell population of three rows on awide body, e.g. a Boeing 767 or 200, could include 21 seats. Aworst-case demand for bandwidth is likely to be for users requestingstreaming video services. While systems using 802.11b protocol have beendemonstrated to provide up to 8 Mbps per access point, a bandwidth of 6Mbps is assumed to be achievable on a repeatable basis using standardhardware components. Thus it is assumed that a maximum aggregatebandwidth of 6 Mbps is available per access point 18 using shorttransmission preambles, and that typically 30 percent, i.e. 6 or 7 userPEDs 38, in a cell 80 are active and sharing the 6 Mbps bandwidth. Lessbandwidth-demanding services such as e-mail or Internet access cansupport more users per access point 18. It is contemplated that powerradiated by components of the WLAN 10 is kept in the 1- to 5-mw range inorder to meet interference, health and safety requirements.

Received Signal Strength

Table 4 below describes 2.4 GHz WLAN radiated emissions at transmitpowers from 1 to 100 milliwatts and at a transmitter-to-victim distanceof 3 meters. Assuming a maximum distance of 3 meters between an accesspoint and its cell boundary, as shown in Table 4, a user PED 38 at themaximum distance from an access point antenna 34 broadcasting at 1milliwatt receives a signal in the range of −45 to −50 dBm. This signalexceeds the 802.11b-specified value of −76 dBm required to support 11Mbps communication. Such margin protects against signal fading due tomulltipath within the aircraft cabin.

TABLE 4 2.4 GHz WLAN Radiated Emissions Victim to Transmitter Distance =3 m lambda = 0.125 m Assume Tx antenna gain (dBi) = 2.2 = numeric EffArea = 0.001875 m{circumflex over ( )}2 1.659587 short dipole Trans- mitTx Power Tx Field Tx Field Received Power Density Strength StrengthReceived Power (mw) w/m{circumflex over ( )}2 v/m dBuv/m Power w dBm  1 1.4674E−05 0.074378 97.42889 2.75E−08 −45.60451  3 4.40219E−05 0.128826102.2001 8.25E−08 −40.8333  5 7.33698E−05 0.166314 104.4186 1.38E−07−38.61481 10 0.00014674  0.235204 107.4289 2.75E−07 −35.60451 200.000293479 0.332629 110.4392  5.5E−07 −32.59421 30 0.000440219 0.407385112.2001 8.25E−07 −30.8333 50 0.000733698 0.525932 114.4186 1.38E−06−28.61481 100  0.001467397 0.74378  117.4289 2.75E−06 −25.60451

RF Susceptibility Test Levels For Aircraft Equipment

Aircraft systems have been qualified to varying RF susceptibility testlevels and frequency ranges. Those systems that have been determined tobe flight-critical and essential are required to demonstrate immunity tothe effects of High Intensity Radiated Fields (HIRF) and have beentested to field strengths that are many orders of magnitude above the RFfield strength generated by an 802.11b WLAN system. Other systemsqualified to levels below the HIRF levels also have demonstrated RFimmunity in the 2.4 to 2.483 GHz frequency range. For any aircraftsystem for which there is no radiated susceptibility test data in the802.11b operating band of 2.4 to 2.483 GHz, it is proposed that aircraftlevel susceptibility testing be performed to demonstrate that there willbe no interference from the worst case operation of an 802.11b wirelessLAN configured in accordance with the embodiments described herein.

The above-described WLAN 10 includes multiple intentional RFtransmitters that operate at very low levels of RF field strength. Theselow levels provide significant margins of compliance for bothelectromagnetic interference and RF exposure limit regulations foroperators, airframe manufacturers, and the traveling public. This makesit possible to safely operate the above-described WLAN 10 on boardcommercial aircraft in flight.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A wireless local area network adapted for use by users traveling on amobile platform, wherein the mobile platform has a plurality of rows ofseats, the network comprising: a network server located on the mobileplatform; a plurality of network access components each independentlyassociated with a specified seating area on the mobile platform, eachbeing in communication with the network server, and each network accesscomponent being accessible wirelessly by a predetermined number ofportable electronic devices; each of said network access componentsincluding an antenna; at least first and second ones of the networkaccess components further being located at spaced apart ones of saidseat rows in the mobile platform; and each of the network accesscomponents further being configured to wirelessly communicate via itsassociated said antenna with said portable electronic devices within anassociated one of said seating areas on the mobile platform whileenabling roaming of a given one of said portable electronic devicesbetween said first and second ones of the network access components; anda communication system for wirelessly linking said network server onsaid mobile platform with a subsystem disposed remotely from said mobileplatform.
 2. The wireless local area network of claim 1, wherein thenetwork access components are each operably associated with at least onespaced apart seat row.
 3. The wireless local area network of claim 1,wherein adjacently positioned ones of said network access points operateon non-overlapping frequency channels.
 4. The wireless local areanetwork of claim 1, wherein each of the network access components isconfigured to transmit and receive signals using a spread-spectrummodulation method.
 5. The wireless local area network of claim 1,wherein each of the network access components is configured to provide awireless communications link to only ones of said portable electronicdevices that meet a predetermined standard for electromagneticinterference.
 6. The wireless local area network of claim 1, whereineach of the network access components is configured to provide awireless communications link to only ones of said portable electronicdevices that meet a predetermined standard for at least one of healthand safety.
 7. A wireless local area network adapted for use by userstraveling on a mobile platform, wherein the mobile platform has aplurality of rows of seats, the network comprising: a network serverlocated on the mobile platform; a plurality of network access componentseach forming a network access point, and each being independentlyassociated with a different, predetermined seating row on the mobileplatform, and each being in communication with the network server; eachsaid network access component being accessible wirelessly by at leastone portable electronic device located in its associated said seatingrow; each of said network access components including an antenna; eachof the network access components further being configured to wirelesslycommunicate via its associated said antenna with said portableelectronic devices within an associated one of said seating rows on themobile platform while enabling roaming of a given one of said electronicdevices between said different ones of said network access components;and a communication system for wirelessly communicating informationbetween said network server on said mobile platform and a subsystemdisposed remotely from said mobile platform, said communication systemincluding a receive antenna and a transmit antenna.
 8. The wirelesslocal area network of claim 7, wherein each said network accesscomponent provides wireless coverage for ones of said personalelectronic devices that are located in a plurality of rows of saidseats.
 9. The wireless local area network of claim 7, wherein each saidnetwork access component is located overhead in a cabin area of themobile platform.
 10. The wireless local area network of claim 7, whereineach said network access component provides a wireless coverage regionfor covering all of the seats in a given row of said seats within themobile platform.
 11. The wireless local area network of claim 7, whereinadjacently positioned ones of said network access points operate onnon-overlapping frequency channels.
 12. The wireless local area networkof claim 7, wherein each of the network access components is configuredto transmit and receive signals using a spread-spectrum modulationmethod.
 13. The wireless local area network of claim 7, wherein each ofthe network access components is provides a wireless communications linkto only ones of said portable electronic devices that meet apredetermined standard for electromagnetic interference.
 14. A wirelesslocal area network adapted for use by users traveling on a mobileplatform, wherein the mobile platform has a plurality of rows of seats,the network comprising: a network server located on the mobile platform;a plurality of network access components each forming a network accesspoint, and each being independently associated with a different,predetermined group of seating rows on the mobile platform, and eachbeing in communication with the network server; each said network accesscomponent being accessible wirelessly by at least one portableelectronic device located within its associated said group of seatingrows; each of said network access components including an antennalocated in an overhead area of a cabin of said mobile in which said rowsof seats are located; each of the network access components furtherenabling roaming of a given one of said electronic devices between saiddifferent ones of said network access components; and a communicationsystem for wirelessly communicating information between said networkserver on said mobile platform and a subsystem disposed remotely fromsaid mobile platform, said communication system including a receiveantenna and a transmit antenna.
 15. The wireless network of claim 14,wherein each of the network access components transmits and receivessignals using a spread-spectrum modulation method.
 16. The wirelessnetwork of claim 14, wherein each of the network access components islocated in an overhead area within a cabin area in which said seat rowsare located.
 17. The wireless network of claim 14, wherein adjacent onesof each of the network access components operate on non-overlappingfrequency channels.
 18. The wireless network of claim 14, wherein eachsaid network access point is configured to operate with a predeterminedmaximum number of said personal electronic devices at any given time.